The invention relates to a telephoto camera lens, the focal length of which can be varied by putting together two different lens systems.
Feinwerktechnik & MeBtechnik 98 (1990) 4, p. 167 et seq. discloses a lens comprising four lens elements for micro readers which is able to be modified by partial standardization and variation of components to form comparatively inexpensive lenses with focal lengths which are not all that dissimilar to one another. In the case of the well-corrected lens, the lens elements and separations which are characterized by these features are fixed, whereas the other lens elements and separations are used for variation for other focal lengths. To be specific, of the four lens elements of the lens, the cemented rear member, formed by two lens elements, is held fixed and the two front elements are varied. In this way, the focal range can be extended with good imaging characteristics from 29.9 mm to 45.4 mm. Due to the use of the same molded blanks and lower unit costs of the lens elements not to be varied, the production expenditure for new focal lengths is reduced within a certain, limited range.
EU 0 262 421 B1 discloses a projection lens of variable focal length which has a front member comprising a single lens element of negative refractive power and a three-element basic lens of positive refractive power, between which a multi-element variator of positive refractive power which can be displaced in the direction of the optical axis is arranged. In this case, one and the same variator can be used for lenses of different focal ranges, so that only a single mold set is required in quantity production.